<vaadin-router> DOM API (basic functionality)

[vlukashov]

As a developer I want to display different content on the page depending on the current URL.

As a Polymer developer I want to do that with HTML markup.

DoD:

• the <vaadin-router> DOM API allows creating a router with a default router outlet, and setting a routes config with <vaadin-route> elements.
• The route contents can be defined by a 'component' property on a <vaadin-route> element.
• The route content can be defined by a <template> child of a <vaadin-route> element.
• Changes to the DOM are handled and trigger a re-render if necessary:
  -- changes to the 'path' and / or 'component' properties / attributes
  -- adding / removing the child <template> element to a <vaadin-route>
  -- adding / removing child <vaadin-route> elements to a <vaadin-router>
• add a demo for basic <vaadin-router> DOM API usage
• the following snippet should work:

<vaadin-router>
  <vaadin-route path="/">
    <template>
      <h1>Home</h1>
    </template>
  </vaadin-route>
  <vaadin-route path="/users" component="x-user-list"></vaadin-route>
</vaadin-router>

The common DoD applies.

[vlukashov]

Won't fix.